Always directly watch them when they are together. That's the first thing. And then you have to punish the rough behavior. I know it may not be intentional, but she has to learn that your baby is not a baby *doll*. That was a hard lesson for my daughter too, when my son was born. I think constant reminders that the baby isn't a doll was helpful. But either way, whether the harm is intentional or not, your daughter still needs to learn consequences.

Shes a bit young to be by herself with the baby. She just doesnt know she can actually hurt him and sounds like she is playing. When my sister was 3 she thought me throwing her around (but we were in a pool) was the funnest thing in the world. flying in the air then back into the water. She loved it! But obviously 8 months is way too young. but I agree with @LadyGwenivere@xanga -  on the no touch rule. That sounds like a pretty good one.

I'm trying to figure it out myself. My son who is 4 is really mean to my daughter who is 1. Hes always pushing her down or trying to smack her. I may try the hands to yourself thing, maybe that will work. We already tried putting him in the corner, & other forms of punishment but none of it works. He just really doesnt like his sister, hes always saying he hates her. I know siblings fight but its horrible.

I have a 4 year old, 3 year old, and 1 year old, so I can totally relate.  It's a little unrealistic to think you can have your eyes on the two of them ALL the time.  So, you have to put an end to the rough behavior.  My oldest daughter used to try to play peek-a-boo with my youngest.  I scared the living daylights out of her by explaining that a baby could die if she accidentally suffocated her.  I also gave time-outs for any rough behavior I witnessed.  It didn't take long before the behavior stopped.

ok, I have to say this. I am not anti-spanking (but it has to be for a dang good reason like running away from mommy and daddy) but some people are suggesting spanking for one child having hands on another child. If you do this, you will just confuse the poor kid!!!
Think about it for a minute, you are trying to teach "Hands to yourself" to a young child. They go and play rough with their sibling, and you put your hands on them (spanking) as punishment. You are trying to teach your child that hitting is not ok and the punishment is hitting them? Confusing!!
The best (and in my opinion ONLY) way to teach "hands to yourself" is to use time outs (and I am one who thought time outs didn't work! they do!). It took 3 days to get this into my son's brain. And there was about 2 hours straight where I'd catch him trying to pick up his sister, he'd get a time out. Literally 2 minutes after getting out of time out he'd be doing something else. So, right back in. Man was I ready to scream, but I refused to budge and I was going to be consistent if it killed me. It worked!

@Aletheas_Unspoken_words@xanga - Our kids are the same age! cool =) The hands off rule works, but you really have to be consistent. My son told me that too, that he hates his sister.  That is nothing but something to get a reaction from mom. I found what really helped with his behavior was special 1 on 1 time with me and daddy. So when the baby is sleeping i make a point of being with him, and then Wednesdays he gets his night out with daddy at Awana. He is jealous and needs some extra loving. It will pass =)

Give her rules....

My son was 5mos old when my 24mo old daughter dislocated his elbow because she pulled too hard when she was "dancing" with him. I was two feet away and it happened in a split second. I was dancing with them both when the phone rang. I got up to answer it and didn't whenever make it to the phone when I heard him scream. It was a quick fix fortunately, and apparently can happen very easily for some kids. But moral of the story, keep the baby out of the toddler's reach! Pack n Plays or play pens are very handy.